This year we had an opportunity to run a field trial on a sward of Kentucky bluegrass on this campus. The sod was laid in summer 2014, and summer patch symptoms were evident 12 months later. I first wrote about this observation several months ago. A variety of fungicides were applied to the site in replicated plots (with post application irrigation), similar to trials conducted at our turf research center. Also, our grounds manager applied supplemental N (equivalent to 22 lb N per acre) prior to our fungicide sprays. The image in Figure 1 shows the site at the time of the fungicide application (July 29).
Figure 2 shows the site on August 18. It is interesting that the turf seems to have recovered—or at least the damage is masked by accelerated growth of the Kentucky bluegrass. Close inspection reveals the depressions in the sod where grass had been killed, or slowed growth to such an extent that the surface is quite uneven (Figure 3). Also interesting is that there are no obvious rectangular patterns of different turf where our fungicide trial was established. The fungicide products include all of the modern compounds that are quite effective in limiting growth of summer patch and necrotic ring spot pathogens. One might have expected some contrast between check plots and those treated with fungicides. However, fungicides had no effect on visual turf quality.
Figure 4 shows the site as it appeared on October 12. The turf remains green but the surface is rough. I imagine if mowing height was reduced to one inch, the patches would be much more apparent. Also, there are no signs of differences in growth from our fungicide trial.
So, is there a take home message here? We must be careful about drawing conclusions from observations made at one site, in one year. These observations fit into the category or “anecdotal information”. It is clear that supplemental N helped mask damage and improve visual turf quality. Applying N in mid-July in the lower Midwest can be risky since other diseases may threaten. Two issues worked in our favor. First, Kentucky bluegrass is not prone to many summer foliar diseases that threaten other turf species and, second, the summer of 2015 was relatively mild, with only a few days reaching 90°F from June through September.
This is a valuable demonstration of the negligible effects of fungicide applied when summer patch symptoms were in full bloom. I am not surprised at the result. It supports the strategy of a preventive approach for disease control—especially where root diseases are concerned. Stay tuned—we plan on another fungicide trial in the spring of 2016!